The family of a US government scientist who fell to his death from a New York hotel window six decades ago have launched a lawsuit for damages against the CIA, alleging the agency was involved in his murder and a subsequent cover-up.

In one of the most notorious cases in the organisation’s history, bioweapons expert Frank Olson died in 1953, nine days after he was given LSD by agency officials without his knowledge.

In the lawsuit, filed in the US district court in Washington on Wednesday, Olson’s sons Eric and Nils claim their father was murdered after he witnessed extreme interrogations in which the CIA killed suspects using the biological agents he had developed.

The CIA has long denied any foul play, though it was forced to admit in 1975, more than 20 years after the death, that the scientist had been given LSD in a spiked glass of Cointreau. The agency, which originally told the family the death was a result of job-induced stress, has since maintained that it was a drug-induced suicide.